1. Field of the Invention
This invention relates to battery vent plugs and in particular to battery vent plugs provided with low pressure relief valves.
2. Description of the Prior Art
In U.S. Pat. No. 3,201,284 of Grenville B. Ellis, a vent valve for batteries is shown having a pair of seal rings provided with abutting tapered annular portions which are deflected from their normal abutting association by pressure acting outwardly through a vent passage communicating with the interior of the battery. The rings are carried in an outwardly opening annular groove on the body of the plug so as to vent the battery to atmosphere through the resulting opening therebetween.
Robert A. Warren et al, in U.S. Pat. No. 2,934,584, show a control vent having a resilient sealing disc engaging the edge of a cup containing the battery cell elements, and means for clamping the disc against the cup edge. A gap is provided in the edge so that sealing pressure is exerted by the resilient strain of the less combined portions of the sealing disc adjacent the gap so that pressurized gas may lift the edge of the sealing disc at the gap and escape from the cup.
In U.S. Pat. No. 3,096,216, Robert A. Warren shows a vent valve adapted for venting an alkaline cell at gas pressures of 135 lbs. psi. The valve includes a sealing disc lying over a groove or notch, which is pushed slightly into the notch by the high pressure. By urging the sealing disc portion sufficiently into the notch, the seal with the sealing cup is momentarily broken to permit gas to escape.
Robert A. Warren discloses, in U.S. Pat. No. 3,114,659, a valve wherein a nylon gasket, a steel diaphragm, and a neoprene gasket are caused to bow outwardly by the pressure of the gas. When a certain predetermined pressure is reached, the seal between the sealing cup and the neoprene gasket is weakened sufficiently to permit venting therebetween. Upon reduction of the pressure, the steel diaphragm urges the structure back to the normal position, reestablishing the seal.
A common problem in the known battery pressure relief valve is the reduction of the pressure within the valve substantially to ambient or zero psig, as a result of each pressure relief operation. Thus, it is conventional in the known pressure relief valves to permit continuous bleeding until internal pressure in the battery reaches zero. A number of prior art vent devices which tend to maintain an internal pressure at all times have a relatively high relief pressure. One such structure is defined by a rubber disc with a narrow slit in the center thereof.